Motor vehicles may use a single power steering pump to provide both steering and braking assist, where the pump regulates hydraulic flow and limits pressure to ensure that steering and braking systems can meet peak demand requirements. Such systems, however, can use large amounts of excess energy during non-demand situations. Thus, when the system does not provide assist to the brake system and/or steering system, it is common to reduce pump output during low demand conditions. However, when the system is required to provide brake assist and/or steering assist, it operates at a higher output level to assure availability of adequate braking assist.
One known approach for controlling such a system in a vehicle having stop-start engine capability uses detailed driver braking demand information to control the hydraulic pump. Specifically, the known system includes a brake-by-wire system, and uses brake sensor inputs that provide detailed information as to the level of brake actuation requested by the driver, such as the degree of driver depression.
However, the inventors herein have recognized several disadvantages of the above system. As one example, it relies on detailed brake information that may only be available on systems utilizing complex brake-by-wire systems, such as in hybrid vehicles having stop-start functionality. As another example, detailed brake information may be unavailable in some systems which may otherwise benefit from adjustable pump control to provide both braking and steering assist functions. As still another example, adding complex braking control or detailed sensor systems may undesirably increase system cost.
Thus, in one approach, at least some of the above issues may be addressed by a method to control a hydraulic pump of a vehicle, the pump coupled to at least a power steering system and a power braking system, the method comprising: measuring steering and braking information using a brake sensor and a steering sensor; and adjusting output of said hydraulic pump based on measured information from said sensors. For example, the method may use predicted pump demand to control a hydraulic pump and adjust output of said hydraulic pump based predicted pump demand using measured information from sensors.
In this way, it is possible to advantageously control the pump to generate appropriate flow rate to handle both steering and braking maneuvers, while also reducing parasitic losses without the need for additional sensors.
In another approach, a system for a vehicle having a power steering and a power brake system may be used. The system comprises: a pump coupled to at least the power steering and the power brake system; a brake switch sensor configured to indicate whether or not a brake pedal of the brake system is actuated by a vehicle operator; a hydraulic brake booster hydraulically coupled to the pump and mechanically coupled to the operator actuated brake pedal; a steering sensor coupled to the steering system; and a control system configured to adjust output of the pump in response to said brake switch sensor and said steering sensor.
In this way, it is possible to advantageously utilize a lower resolution brake sensor system having lower cost components, such as a hydraulic brake booster, while still providing appropriate control of a hydraulic pump that provides both steering and braking assist. For example, by utilizing both steering and brake sensor information, sufficient assist operation may be provided to the steering and braking systems when needed, while also reducing parasitic system losses when such assistance is not needed.
Note that various types of steering sensors may be used, such as steering angle, steering rate, steering torque, combinations thereof, and others. Further, various types of brake sensors may be used, such as a brake switch, a brake light switch, a brake pressure switch, combinations thereof, and others. The pump may be driven by an electric motor, driven by the engine (e.g., via the front end accessory drive, FEAD), combinations thereof, or others.